In cellular systems for wireless communication, base stations of different kinds are normally used. A typical base station (BS) in a cellular system is often deployed above roof-top level or in a high mast, increasing its coverage area. In the mast, there are normally a number of antenna units, single polarized or double polarized, that each provides sector coverage for a certain cell area or sector area. Typically, three antenna units are placed equidistantly around the circumference of the mast, such that each antenna unit covers a 120° sector, thus these antenna units have three corresponding successive sector areas.
It is of interest to attain isolation between such neighboring sector areas.
Antenna polarization can be utilized to provide isolation between signals transmitted or received in such neighboring sector areas in a wireless cellular communication system. By ensuring that transmitters in neighboring sector areas have orthogonal polarizations, it is possible to improve the isolation between the signals in a receiver, resulting in less interference between the cells.
However, the number of antenna polarizations to choose from is limited. Typically, there are only two orthogonal choices possible for a sector-covering or omni-directional base station antenna. This severely limits the usefulness of the antenna polarization as a means for improved isolation or coverage as outlined above. The typical cellular site being equipped with three sector-covering antennas as described above makes it impossible to choose antennas such that all three are orthogonal towards each other.
Additionally, each cell can have multiple neighboring cells where the mutual interference among these can not be adequately suppressed with the degrees of freedom of only two polarizations.
There is thus a need for a base station antenna arrangement, where the isolation between the cell areas or sector areas that are covered by a certain base station is improved.